The present invention relates, generally, to the field of computer graphics. Computer graphics display systems, e.g. CAD/CAM graphics workstations, are widely used to generate and display images of objects for scientific, engineering, manufacturing and other applications.
In such computer graphics systems, surfaces of an object are usually represented by a polygon mesh. A polygon mesh is a collection of vertices, edges, and polygons. The vertices are connected by edges, while polygons can be thought of as sequences of edges or of vertices. To present a visual image of an object on the viewing screen of the display which is more realistic in appearance than the corresponding polygon mesh, procedures have been developed for removing hidden surfaces and shading and adding texture to visible surfaces.
The present invention relates to implementation of a shading function in a graphics workstation and more specifically to the computer processing and display of shaded images in which a lighting model is used. Effects which may be taken into account in such a lighting model include ambient lighting, diffuse and specular reflection effects, the number, position, intensity and hue of the light sources, parallel and perspective projections, and attenuation of the light due to the distance of different portions of an object being modeled from the viewer (depth cueing).
The general system architecture of shading hardware for a graphics workstation is depicted, in block diagram form, in FIG. 1. The overall shading function system 10 includes a lighting model processing system 12, a shading processing system 14, a video pixel memory 16 and a display monitor 18.
The lighting model processing system 12 calculates the color intensities (e.g. red, green and blue components) at the vertices of each polygon for a specified lighting model. The shading processing system 14 uses the information from the lighting model processing system to calculate the color intensities of pixels interior to visible polygons and sends this information to the video pixel memory 16. The display monitor 18 displays the shaded image stored in the video pixel memory.
In prior graphics workstations, calculation of the effects due to lighting has been performed by some type of general purpose processor. This approach, while having the advantage of using commonly available "off the shelf" components, suffers the disadvantage of being slow, since the entire process is performed by a single general purpose processing element.